1. Field of the Invention
The present invention relates to a bonding surface structure provided with bonding layers and to a bonding structure having the bonding surface structure.
2. Description of the Related Art
FIG. 1 shows a cover 1 and a frame 3 for a card having a conventional bonding surface. The cover 1 is a component of an IC card, such as a PC card or a CF card, and includes a plate 1a which is made of a metal or insulating material. The plate 1a has a single bonding layer 4, to be bonded to the frame 3, on the peripheral portion 2 thereof. The bonding layer 4 is activated by, for example, heat, to bond the cover 1 to the frame 3 by thermocompression.
There are various types of bonding materials including bonding agents and bonding sheets or films, and the bonding layer 4 is formed of one of the bonding materials. For example, the bonding layer 4 is formed of a polyester-based bonding material A or a polyester-polyamide-based bonding material B, which have properties shown in Table 1.
The tensile shear bond strength in Table 1 indicates the tensile shear strength when the bonding layer is formed on a stainless steel sheet.
As shown in Table 1, the polyester-polyamide-based bonding material B is resistant to heat to a greater extent than the polyester-based bonding material A, whereas the polyester-based bonding material A has a tensile shear bond strength which is higher than that of the polyester-polyamide-based bonding material B. When the bonding layer 4 is formed using the polyester-based bonding material A, the bonding between the cover 1 and the frame 3 is resistant to impact, but the bonding strength decreases in a high-temperature environment, resulting in separation between the cover 1 and the frame 3. When the bonding layer 4 is formed using the polyester-polyamide-based bonding material B, the cover 1 and the frame 3 are barely separate in a high-temperature environment, but will be readily separated by an impact. Thus, no bonding layer 4 is resistant to both high-temperature environments and to impacts.
The bonding layer 4 must simultaneously have different properties, for example, high resistance to both high-temperature environments and high impact resistance, in order to ensure reliability of bonding of the IC card.
It is an object of the present invention to provide a bonding surface structure which can improve reliability of bonding of a product and to provide a bonding structure having the bonding surface structure.
In a first aspect of the present invention, a bonding surface structure includes at least two types of adjoining bonding layers having different chemical components formed in a bonding layer forming region.
In the bonding surface structure, a gap is preferably provided between the bonding layers to prevent mixing of the different chemical components.
Alternatively, a barrier is preferably provided between the bonding layers to prevent mixing of the different chemical components.
In the bonding surface structure, the bonding layers are preferably capable of being activated by heat.
Preferably, the bonding layers are formed by a printing process.
In a preferred embodiment, the bonding layer-forming region is a bonding layer forming region of a cover which covers a surface of an IC card.
In a second aspect of the present invention, a bonding structure including a bonding surface structure according to the first aspect, wherein an indented portion is formed on a bonding surface of a counter member with respect to the bonding layer forming region, and at least two bonding layers are overlaid so as to protrude at the position in the bonding layer forming region corresponding to the indented portion so that the indented portion is filled with the protruded bonding layers when the bonding layer forming region is bonded to the bonding surface of the counter member.
In a preferred embodiment of the present invention, for example, bonding layers composed of a bonding material, which is resistant to high-temperature environments but is not resistant to impacts, and bonding layers composed of another bonding material, which is resistant to impacts but is not resistant to high-temperature environments, are alternately formed in a bonding layer forming region. Thus, the entire bonding surface structure is resistant to both high-temperature environments and to impacts.
The bonding surface structure of the present invention can simultaneously satisfy a plurality of requirements by selecting a plurality of bonding layers satisfying the requirements. As a result, a product having this bonding surface structure is highly reliable in various environments.